One of the major problems confronting our society today is the generation of wastes. Landfilling had become the method of choice with the prevailing mentality being "Out of Sight--Out of Mind!". The most commonly considered alternatives to landfills are mass incineration of municipal waste and its related activity, the production of refuse derived fuel (RDF). Incineration and refuse derived fuel produce a variety of pollutants that cause respiratory discomfort and disease. These pollutants are caused by incomplete combustion of municipal solid waste and the oxidation of plastics in the presence of metals.
It is known that municipal solid waste contains many materials of value, when recycled. Environmentalist and public officials view the recycling of these materials as the most desirable method of waste disposal; however, present recycling efforts have reduced the volume of MSW by less than ten percent.
In light of the shortcomings, both technically and economically of mass-burn and refuse derived fuel and with an awareness of the wealth of recyclable materials being lost in landfills, a method of easily classifying and separating recyclables is needed.
In my prior U.S. Pat. No. 4,342,830, dated Aug. 3, 1982, steam treatment of MSW is disclosed wherein the sterilized and softened organics are forced through perforations upon sudden release of pressure whereby inorganics and certain synthetics, such as metal cans, glass, plastic containers and the like, are left behind. This method was aimed at the production of ethanol and included the addition of significant quantities of water to the wastes and thus required substantial energy consumption in the form of steam to heat the water/waste slurry, transform it into a pulp and to force the resultant sterile and pulped organics through the perforations in a singular step. The pulped organics were intended primarily for ethanol and animal food production. The plastic recovered which were suitable for recycling were generally less than 2% of the waste by weight and were generally severely contaminated with softened organics and dirt. The inorganic materials such as ferrous and non-ferrous metals were also similarly contaminated, making these products less desirable for recycling. The glass components were both broken and contaminated.
In my prior U.S. Pat. No. 4,540,495, dated Jun. 10, 1985, steam treatment was again disclosed wherein the amount of water added prior to steam treatment was significantly reduced to conserve energy consumed and to limit the residual moisture content of the softened organic fraction to the order of 60%-70% by weight.
Further test have proven the stated water added to the final moisture content of the pulp (in my U.S. Pat. No. 4,540,495) is necessary to ethanol production but is not necessary for other uses. For example, it is not essential to have a 60%-70% moisture content in the pulp for effective screening. Tests have proven that effective screening can be accomplished at final moisture content ranges as low as approximately 30%-40%. If desirable, the pulped material can be screened when completely dry.
There was no method disclosed in my U.S. Pat. No. 4,540,495 for controlling final moisture content of the softened organic fraction; therefore, making final separation more difficult and decreasing the desirability of the plastics, and inorganic recyclables. However, further test have proven that lower residual moisture content than that stated facilitates easier separation of the processed waste components. It has also been determined by further testing that efficient heat-mass transfer and efficient mixing are not limited by the 70% ratio of input volume and vessel volume as stated in my U.S. Pat. No. 4,540,495.
Time, moisture content, pH, pressure, temperature and viscosity are all essential variable to be adjusted to determine the final condition of the processed waste. The addition of surfactants, acids, caustic, moisture, heat, vacuum, and varying the length of the mixing period are all steps that may be taken to achieve the desired end result. Actual application of the prior patent parameters revealed that the internal steam pressure requirements in combination with the resultant temperatures and the necessary period of time required to "cook" and sterilize the waste material and soften the organic matter also caused a melting of many of the plastics and significant heat distortion of most other plastics as in the previous U.S. Pat. No. 4,342,830.
Also in my prior U.S. Pat. 4,844,351, primarily, a method for separation, recovery, and recycling of plastics from municipal solid waste was disclosed wherein mixed wastes including various plastic elements were subjected to mechanical agitation and heat distortion. The wastes were introduced into a processing unit having a means for heating and a means for agitating the wastes. By this method, the plastics were recovered as a mixture that may be recycled, but due to lack of control of the variables as mentioned above, the cellulose residuals were less than desirable. As set forth herein, by controlling pH and other variables, the moisture content and heat may be reduced to yield cellulose to customized specifications, yet leave the plastic in a form that is recyclable.
The above noted defects of the prior art are overcome by the method and structure of the present invention which overcomes the deficiencies of the prior inventions as set forth above and provides an efficient process for the treatment of municipal solid waste (MSW). The waste materials are introduced into a pressurized, heated, rotatable pressure vessel and subjected to controlled conditions wherein a fluid is injected into the pressure vessel and the amount of moisture, the pH level, caustic environment, the viscosity of the fluid, the temperature and the pressure is controlled as the waste material is tumbled and mixed to substantially "fluidize" or pulp the organic material thus making it more easily separated from the inorganic materials such as glass, metals, etc.
The moisture inside of the vessel has its pH controlled by the addition of an acid into the vessel. The viscosity of the moisture environment is controlled by the addition of a surfactant into the vessel to control the surface tension of the materials in the vessel. The caustic substances (such as sodium, hydroxide or the like) may be added to control the chemical disintegration of some waste materials in the vessel.